A heteromorphism in a pair of macrochromosomes in male Siebenrockiella crassicollis is interpreted as an XX/XY sex determining system. The heteromorphism involves a difference in centromere position and amount and distribution of heterochromatin. The only other sex chromosome system known in turtles is found in the kinosternid genus Staurotypus and is also an XX/XY system, but it involves a different chromosome pair and different chromosomal rearrangements. These two systems have independently… CONTINUE READING